A vacuum gate valve of a one-action type is known for instance as a vacuum gate valve that is used for a semiconductor manufacturing apparatus or the like.
FIG. 9 is an exploded perspective view showing a vacuum gate valve of a one-action type.
More specifically, for a structure of a vacuum gate valve 100, a valve plate 102 carries out a linear movement in a single direction by a force applied from an actuator 104, thereby sealing a gate opening portion 106 in an almost rectangular shape.
For the vacuum gate valve 100, an O ring 108 having a circular cross section is used in general as a sealing material mounted on a peripheral face of the valve plate 102.
In some cases, the vacuum gate valve 100 is used for a load lock chamber in which a pressure reduction and an atmospheric release are repeated in order to transfer a substrate inside or outside in a semiconductor manufacturing apparatus or an FPD manufacturing apparatus, etc.
In the case in which a load lock chamber is released to the atmosphere in the state in which a valve body of the vacuum gate valve 100 is closed, a differential pressure of one atmosphere is applied to the valve body and the valve body is moved in the direction opposite to the load lock chamber while the valve body is closed. When a pressure reduction of the load lock chamber is carried out again, the valve body is moved again to the load lock chamber side. As described above, for the vacuum gate valve 100 mounted to the load lock chamber, the valve body is moved in a horizontal direction at frequent intervals due to the configuration of the apparatus.
For instance, as shown in FIG. 10, in the case in which the valve plate 102 is moved repeatedly in the arrow direction, a resultant force of a sealing load and a thrust load is repeatedly applied to the O ring 108. Consequently, torsion occurs in a part of the O ring 108 and a sealing failure occurs easily.
A shape of the O ring 108 having a circular cross section causes a rolling motion easily, thereby causing the O ring 108 to drop out from a sealing groove 112. As described above, for the vacuum gate valve 100 provided with the O ring 108 that easily causes a sealing failure due to torsion or dropping out, a maintenance operation for exchanging the O ring 108 is required at frequent intervals. The maintenance operation stops a production line temporarily, thereby causing a great loss in productivity and an increased cost.
On the other hand, in the case in which the O ring 108 is used and the vacuum gate valve 100 is enlarged according to a growing in size of a processed material such as a silicon wafer, it is necessary to allow a processing accuracy and a fabrication error. Consequently, a cross sectional shape of the O ring 108 must be also enlarged.
In the case in which the vacuum gate valve 100 is enlarged, a load for obtaining a compression amount to the O ring 108 is enlarged. As a result, it is necessary to increase a rigidity of a valve casing 110 and to heighten an output of the actuator 104 in order to increase a pressing force, thereby greatly causing a cost to be increased.
In recent years, some applicants provide a sealing material of a special deformed product in place of the O ring having a circular cross section and a sealing material for a dovetail groove in which the sealing material of the special deformed product is mounted and disposed in the dovetail groove.
FIG. 11 shows a sealing material 200 for a dovetail groove filed by the present applicant. For the sealing material 200 for a dovetail groove, an O ring having not a circular cross section but a deformed shape is adopted to prevent the O ring from dropping out and rolling (see Patent document 1: Japanese Patent Application Laid-Open Publication No. 2003-14126).
The cross sectional shape of the sealing material 200 for a dovetail groove includes shapes composed of a flat bottom side 202 disposed on a bottom face 222 of a dovetail groove 220, right and left oblique sides 204 rising at an angle outward from the both ends of the bottom side 202, right and left overhanging portions 206 that are disposed at the ends of the right and left oblique sides 204 and that are close to an opening portion 224 of the dovetail groove 220, a central protrusion 208 that is formed between the right and left overhanging portions 206 and that is protruded upward from the opening portion 224 of the dovetail groove 220, and concaves 210 that are formed between the central protrusion 208 and the overhanging portions 206 and that are depressed inside the tangential line of the central protrusion 208 and the overhanging portion 206.
The sealing material 200 for a dovetail groove has a symmetric cross section and thereby has a rolling prevention effect against a thrust load from the both directions.
In the case in which the sealing material 200 for a dovetail groove is being mounted in the dovetail groove 220, the sealing material 200 may not be upside down in the dovetail groove 220 since the sealing material 200 has a shape in which the bottom side 202 can be easily found.
Patent document 1: Japanese Patent Application Laid-Open Publication No. 2003-14126